This invention relates to an apparatus for processing photographic material. In particular, the invention relates to processing which uses a low volume of processing solution.
Conventional processing of photographic material requires the use of large tanks of processing solutions. Each tank contains a processing solution such as developer, bleach, fixing solution or washing solution. The material is transported through each tank in turn. There is a tendency for the solutions to carry over from one tank to another leading to pollution of the solutions. Conventional processing has several other drawbacks. The temperatures which can be utilised are limited and therefore the process is slow. The composition of the solutions must be stable over long time residence periods in the processing tanks. Replenishment of the solutions is difficult to control. The processing apparatus is also very large due to the number of processing tanks and the apparatus is limited to only one type of process.
To overcome the problems of conventional deep tank processing surface application of the processing chemicals was developed. In previous surface application methods a volume of solution is applied to the surface of the material being processed. However, previous surface application methods have several drawbacks. If the solution applied to the material is just left on the sensitised surface of the material in a static condition the processing will be very slow and inefficient because there is no agitation and by-products accumulate in the material and solution layers, slowing down the processing. This method is also prone to non-uniformity of processing.
It is also known to process the material within a rotary tube. The material to be processed is placed emulsion side facing inwards within the tube. Solution is added and the tube rotated. Large volumes of processing solution (70 ml/sq.ft and upwards) will process the material effectively so long as rotation is not so fast as to cause dispersion of the solution puddle. Rapid rotation of the device is however very desirable to quickly and evenly distribute a given small volume of solution over the whole surface of the material so that processing is uniform from one end to the other. If the rotation is too slow there will be seasoning of the small volume of solution by the front end of the material and processing will be different at the back end of the material. Small volumes of processing solution (50 ml/sq.ft or less) do not properly process film or paper because when the device is rotated, even at low speeds of rotation, the solution puddle is dispersed and spread over the whole surface of the material. Consequently there is no agitation. This leads to several processing defects. Processing is similar to that already described and can be streaky, non-uniform and slow because of local consumption and the production of by-products. There is no surface mixing and chemical economy is therefore low.
Co-pending application GB 0023091.2 discloses a processor having a cylindrical chamber which is rotated during processing. Film is loaded around the inner circumference of the chamber when the chamber is stationary. One method of loading film into the chamber of the processor is to provide an entry slot in the outer circumference and feed the film through the slot and round the inner circumference. The film is driven by a pair of rollers just outside the entry slot. This method has been described in the above mentioned co-pending application, in which edge guides are also provided to keep the film against the inner circumference and prevent it falling into the centre of the chamber. The edge guides overlap the film edges on both sides by about 2 mm thus providing film retention and also free access of processing solution to the image area and back of the film.
Co-pending application U.S. Ser. No. 09/920,495 (Processing Photographic Material, filed on Aug. 1, 2001, in the name of Twist, Earle, Wildman and Wells) discloses a processor having a cylindrical chamber which is rotated during processing. Film is loaded around the inner circumference of the chamber when the chamber is stationary. One method of loading film into the chamber of the processor is to provide an entry slot in the outer circumference and feed the film through the slot and round the inner circumference. The film is driven by a pair of rollers just outside the entry slot. This method has been described in the above mentioned co-pending application, in which edge guides are also provided to keep the film against the inner circumference and prevent it falling into the centre of the chamber. The edge guides overlap the film edges on both sides by about 2 mm thus providing film retention and also free access of processing solution to the image area and back of the film.
At present the film is fed into the drum chamber through a slot in the outer wall. To seal this and to prevent the solution escaping a rubber door has been used which is opened and closed by a mechanical linkage operated by an electrical solenoid, see FIGS. 1 and 2A and 2B. This system is quite complex and requires a lot of maintenance. In practice the door is worn away very quickly by the film. The door also has been found to leak. The return springs for the linkage also corrode and fail.
The present invention aims to overcome the above mentioned problems.
According to the present invention there is provided an apparatus for processing photographic material, comprising a chamber adapted to hold the photographic material therein, means for introducing processing solution into the chamber, means for removing processing solution from the chamber and means for rotating the chamber, wherein the wall of the chamber has a first end and a second end configured such that the chamber has a substantially circular cross-section, the first end and the second end overlapping by a length sufficient to retain the solution within the chamber during rotation thereof and leaving a narrow channel therebetween, the channel acting as the entrance and the exit for the photographic material.
A processor according to the invention prevents substantially all leakage of solution. This is very important when dealing with the low volumes associated with this type of processor.
As there is no complex mechanical mechanism manufacturing costs are reduced. By reducing the number of parts to the processor the manufacture thereof is simplified, as is the software and operation of the processor.